Medium for increasing the absorption capacity of paper pulp for starch

ABSTRACT

The present invention relates to a medium for increasing the absorption capacity for starch of paper or paper pulp in a fibre slurry for paper manufacture, the medium containing cereal meal and/or starch, in particular rye meal, together with a polymer with vinylamine units.

TECHNICAL FIELD

The present invention relates to a means for increasing the absorptioncapacity of paper pulp, such as is used in paper manufacture, for starchor starch-containing products.

The present invention is suitable for use in conventional methods ofproducing paper, paperboard or cardboard and for devices usually usedfor this purpose, which devices are generally known.

The present invention is especially suitable for manufacture from wastepaper.

BACKGROUND

As a starting material for paper manufacture, an aqueous suspension isprepared from the starting materials such as the fibrous constituentsand optionally other paper auxiliaries. The aqueous suspension willhereinafter be referred to as the fibre slurry, and the solid materialscontained therein as the paper pulp.

For the purpose of improving properties such as the resistance of paperto tearing during the manufacturing process, it is known to add starchas a sizing agent to paper pulp from which sheet paper is ultimatelyobtained.

For paper manufacture, the fibre slurry containing the paper pulp—as yetwithout the starch additive—in suspension, is introduced in the form ofa web on to a band-like sieve which contains dewatering elements. Afterpartial dewatering, the web passes through a so-called sizing press, inwhich the application of starch to the already partially dried web takesplace. In this operation, the starch is applied as an aqueoussuspension, with the result that the moisture content and thus thedrying necessary to achieve the finished, dried paper web is increased.

It would therefore be desirable to already add the starch to the fibreslurry. By this means, the sizing press and the supplementary dryingmeasures could be dispensed with, as a result of which the equipment andthe time required to produce the paper, and thus the cost, could becrucially reduced. Adding the starch to the fibre slurry has alreadybeen experimented with. However, the starch proved to be onlyinadequately absorbed by the paper pulp, with the result that the starchcontent of the paper web obtained is too low to achieve the desiredeffects, in particular increasing the resistance to tearing.

THE INVENTION

The aim of the present invention was therefore to make it possible toalready add starch to the fibre slurry so that the resulting paper webhas a starch content sufficiently high to enable the sizing press andthe associated process control which is also necessary to be dispensedwith during paper manufacture.

According to the invention, this aim is achieved with a medium forincreasing the absorption capacity of paper pulp for starch, whichmedium contains cereal meal and/or starch and a polymer with vinylamineunits, and is obtainable by mixing the cereal meal and/or the starch andthe polymer with vinylamine units in an extruder.

The invention further relates to a method of paper manufacture in whicha medium containing cereal meal and/or starch and a polymer withvinylamine units is added to the fibre slurry.

The invention also relates to the use of a medium containing cereal mealand/or starch and a polymer with vinylamine units for increasing thestarch content of the paper pulp, particularly in the fibre slurry.

Cereal meals contain a high proportion of starch, with possiblevariation in the proportion and composition of the starch depending onthe cereal type.

The meal preferably used according to the invention is a rye meal or ameal of a type of cereal in which the proportion and composition of thestarch corresponds to or is similar to that of rye.

The meal may be a commercially available meal.

Preferably-used starches are rye-meal starch, or a starch which, in itscomposition, in particular its content of amylose and amylopectin,corresponds to or is similar to that of rye starch.

The cereal meal and/or the starch may be added to the medium accordingto the invention in each case either in the pure form or as a mixture.

The medium according to the invention additionally contains a polymerwith vinylamine units.

This may be a homopolymer or a copolymer.

These may be obtained in a way which is known per se, by radicalpolymerisation of N-vinylcarboxylic acid amides and subsequent at leastpartial hydrolysis of the amide functional group to form thecorresponding amine functional group.

Examples of suitable monomers and comonomers, and methods of producingpolymers with vinylamine units may be found in EP 0 553 135 B1, EP 0 758344 B1, WO 98/45536 and WO 00/60167, which for this purpose are referredto in their entirety.

Suitable polymers with vinylamine units are polymers obtained bypolymerisation of N-vinylcarboxylic acid amides of the formula

wherein R, R¹=H or C₁ to C₆-alkyl, alone or in the presence of othertherewith copolymerisable monomers, and hydrolysis of the resultingpolymers with acids or bases with cleavage of the group

and with formation of the vinylamine units of the formula

wherein R has the meaning assigned in formula (I).

Suitable formula (I) monomers are, for example, N-vinylformamide,N-vinyl-N-methyl-formamide, N-vinyl-N-ethylformamide,N-vinyl-N-propylformamide, N-vinyl-N-isopropylformamide,N-vinyl-N-butylformamide, N-vinyl-N-sec.butylformamide,N-vinyl-N-tert.butylformamide, N-vinyl-N-pentylformamide,N-vinylacetamide, N-vinyl-N-ethylacetamide andN-vinyl-N-methylpropionamide, N-vinylacetamide,N-vinyl-N-methylacetamide, N-vinyl-N-ethylacetamide,N-vinylpropionamide, N-vinyl-N-methylpropionamide and N-vinylbutyramide.N-Vinyl Formamide

is preferably used according to the invention.

Copolymers of monomers (I) and (I′) contain, for example,

-   1) 99 to 1 mol-% of N-vinylcarboxylic acid amides of formula (I),    and-   2) 1 to 99 mol-% of other, therewith copolymerisable,    monoethylenically unsaturated monomers.

Examples of copolymerisable, monoethylenically unsaturated monomers arevinyl formiate, vinyl acetate, vinyl propionate, N-vinylpyrrolidone,acrylic acid, methacrylic acid, esters, amides and nitriles of acrylicacid or methacrylic acid, and the C₁- to C₄-alkyl vinyl ethers.

Preferred polymers with vinylamine units are hydrolysed copolymers of

-   1) N-vinyl formamide (I′) and-   2) Vinyl formiate, vinyl acetate, vinyl propionate, acrylonitrile    and N-vinylpyrrolidone, as well as hydrolysed homopolymers of    N-vinylformamide.

The degree of hydrolysis of the N-vinylformamide units in thehomopolymers and copolymers is 2 to 100%, preferably 30 to 100%, andespecially 75 to 100 mol-%. The molar mass of the polymers withvinylamine units has a value of up to 1 million, and is preferablywithin the range 10 000 to 600 000 and especially preferably within arange of 400 000 to 500 000 (determined by light scatter).

Homopolymers, especially of N-vinyl formamide, are preferably usedaccording to the invention.

The preferred homopolymers are completely hydrolysed. As defined by theinvention, the term “completely hydrolysed” also includes substantiallycompletely hydrolysed polymers in the sense that, although thehydrolysis should theoretically run to completion, there may bedepartures therefrom which process controls render unavoidable.

Polyvinylamines which are especially preferred according to theinvention are completely, or substantially completely, hydrolysedhomopolymers of N-vinyl formamide as monomers having a molar mass withina range from 400 000 to 500 000.

A suitable example thereof is marketed by the company BASF under theproduct designation CATIOFAST VFH.

The medium according to the invention preferably contains 5 to 30 wt %,especially 10 to 25 wt %, of polymers with vinylamine units (withreference to the native meal with its natural water content).

According to requirements, the medium may also contain a larger orsmaller quantity of polymer with vinylamine units, provided that thefibre slurry is guaranteed to have the desired starch content.

If the cereal meal is wholly or partially replaced by starch, thecontent data must be adjusted accordingly.

The medium according to the invention may also contain water, whicheither originates from the natural content of the meal or of the starchand/or was added in the course of the manufacturing process and wasincompletely removed during subsequent drying.

According to requirements, the medium according to the invention maycontain additives which may be desirable for paper manufacture.

The medium according to the invention may be obtained by intimate mixingof the ingredients, meal and/or starch, polymer with vinylamine units,water if applicable and optionally other additives.

The mixing preferably takes place in an extruder.

One extruder which is suitable for the extrusion is a co-rotatingtwin-screw extruder. An example of a suitable twin-screw extruder is anextruder such as that marketed by the company Bühler under the productdesignation BCTA.

The extruder may be coupled to a preconditioner.

The extrusion usually takes place at a temperature of 100 to 170° C.,especially of 130 to 155° C.

The extrusion preferably takes place during addition of water. The watermay be added in the liquid state or also at least partially as vapour,for example via a preconditioner. The water is usually added in aquantity of up to 30 wt %, preferably 5 to 20 wt %, with reference tothe meal and/or starch content.

The product obtained by extrusion may then be converted into a formsuitable for use. For example, it may be milled to form a granulate.Beyond this, the particle size of the granulate is not critical. It isusually of the order of 0.5 to a few millimetres, for example of theorder of 0.75 mm.

If required, the extrudate, like the granulate, may be subjected todrying. The drying preferably precedes cooling of the extrudate. Thedrying with cooling may be carried out in the usual way, which is knownper se.

A medium which is preferred according to the invention is obtained byextrusion of rye meal with 10 to 25 wt % of polymer with vinylamineunits, preferably with addition of 5 to 15 wt % of water, in each casewith reference to the rye-meal content.

The granulate, which contains starch and/or a cereal meal modified witha polymer with vinylamine units, is added to the fibre slurry for papermanufacture in a quantity sufficient to adjust the starch content of thepaper pulp to the desired value.

It has been demonstrated that the paper pulp is capable of excellentretention of the starch and/or cereal meal modified with a polymer withvinylamine units, yielding a paper web which has the starch contentrequired for adequate tear resistance. The addition of starch via asizing press can therefore be dispensed with according to the invention.

In the case of a medium according to the invention which contains ryemeal, addition of a quantity corresponding to 3 to 5 wt % of rye mealwith reference to the fibre slurry is sufficient.

The invention also comprises an improved method of paper manufacture, inwhich an adequate starch content of the paper pulp may be adjusted asearly as in the fibre slurry, with the result that application of thestarch to the paper web with the use of a sizing press may be dispensedwith. To this end, medium according to the invention is added to thefibre slurry with the paper pulp for paper manufacture in a quantitysufficient to adjust the desired starch content in the paper web to beproduced or the finished paper web. If, for example, a preferred mediumaccording to the invention is used, which is obtained by extrusion ofrye meal with 10 to 25 wt % of polymer with vinylamine units, it issufficient to add a quantity corresponding to 3 to 5 wt % of rye meal(with reference to the fibre slurry).

In what follows, the preparation of the medium according to theinvention will be explained in greater detail with the use of examples.

A conventional rye meal and, as the polymer with vinylamine units,CATIOFAST VFH of the company BASF were used for carrying out theexamples.

All runs of experimental series 1 to 4 were carried out with a BühlerBCTG extruder with a co-rotating twin screw.

In experimental series 2 to 4, a Bühler BCTC preconditioner wasconnected upstream of the extruder, via which preconditioner theindividual ingredients were fed to the extruder. In selected runs, waterin the form of water vapour was additionally fed in via thepreconditioner (reported separately).

Definitions: N Screw speed (rpm) WW Added water [wt %] PC PreconditionerPolymer Polymer with vinylamine units [wt %], with reference to the mealcontent

Rye meal with its natural water content was used for the series ofexperiments.

Experimental Series 1: Parameter Variation Extruder design series: DNDLHousing diameter (extruder) constant at L/D 40 Meal throughput [kg/h]Constant at 50 Polymer [wt %] 10; 17.5; 25 N [rpm] 100; 85; 70 WW [wt %]5; 10; 15

Conduct of the Experiment: Polymer 10 17.5 25 WW/N 100 85 100 85 70 10085 70 15 1 6 8 10 3 4 5  5 2 7 9 Run 1 2 3 4 5 6 7 8 9 N [rpm] 100 10085 85 85 100 100 70 70 Pulp pressure [bar] 45 50 55 51 50 40 50 50 65Extrusion temperature [° C.] 145 165 151 136 138 136 148 126 138 Cutterspeed [%] 50 H₂O ext. [kg/h] 7.5 2.5 5 5.2 5 7.5 2.5 7.5 2.5 Polymerext. [kg/h] 5.1 5.1 5.1 8.7 12.5 12.5 12.5 12.5 12.5

The throughput of the mixture of meal, water and polymer through theextruder was a constant 50 kg/h for runs 1 to 9.

In runs 1 to 9, the water and polymer fraction was added in two batchesto the mixture to be extruded, part being added prior to introductioninto the extruder and part being added to the mixture in the extruder,in the above table described as “H₂O ext.” and “polymer ext.” In thisseries, the “polymer ext.” was added via housing 2 and the “H₂O ext.”via housing 1 of the extruder, which comprised 5 housings.

Experimental Series 2:

In the runs shown here, the rye meal was introduced at a constant rateof 200 kg/h. The polymer was introduced at a constant 10 wt % of theintroduced meal (20 kg/h).

In runs 4, 5, 6 and 7, water was added in the form of water vapour. Inthe runs with the switch in the “off” position, water (liquid) andpolymer, but no water vapour, were introduced via the preconditioner.

The runs were conducted as follows: PC off >95° C. N WW 10 15 0 5 10 1508 6 7 200 2 3 5 4 250 1 Run 1 2 3 4 5 6 7 8 N [rpm] 250 200 200 200 200150 150 150 Torque [%] 45 54 46 31 36 41 35 49 Pulp pressure 69 87 70 3640 50 44 64 Extrusion temperature [° C.] 155 155 147 146 155 152 148 159PC temperature [° C.] — — — 98 99 99 99 100 Rye meal [kg/h] 200 Water[%] 10 10 15 10 5 5 10 — Polymer [%] 10 10 10 10 10 10 10 10

The granulated extrudate was dried and cooled, during which operation itwas collected in a drier (Bühler OTW 50) for 5 minutes, kept in thedrier for a further 5 minutes and then transferred to a cooler. Aftercooling to room temperature, the granulate was decanted.

Experimental Series 3: PC off >95° C. N WW 5 10 15 0 5 10 150 17 16 1519 20 21 200 13 14 18 250 10 11 12  9 23 24 Run 9 10 11 12 13 14 15 1617 18 19 20 21 22 23 N [rpm] 250 250 250 250 200 200 150 150 150 200 150150 150 250 250 Torque [%] 32 36 42 32 39 35 50 57 58 29 43 38 33 33 28Pulp pressure 90 124 57 104 104 91 87 116 128 46 61 60 47 47 47Extrusion temperature [° C.] 134 163 168 154 149 140 135 146 158 146 156150 144 173 165 PC temperature [° C.] — 95 98 98 98 99 99 Rye meal[kg/h] 200 Water [%] 15 5 5 5 10 10 15 5 5 5 — — 10 — — Polymer [%] 1010 15 15 10 15 10 15 10 15 10 15 10 10 15

The drying and cooling of the extruded granulate was performed as inexperimental series 2.

Experimental Series 4:

The addition of meal was varied for experimental series 4. No. 24Polymer: 10% 250 kg/h 150 rpm No. 25 Polymer: 10% 300 kg/h 200 rpm No.26 Polymer: 10% 400 kg/h 250 rpm Run 24 25 26 N [rpm] 150 200 250 Torque[%] 48 46 55 Pulp pressure 61 63 78 Extrusion temperature [° C.] 151 154157 PC temperature [° C.] 95 93 89 Rye meal [kg/h] 250 300 400 Water [%]5 5 5 Polymer [%] 10 10 10

The drying and cooling of the granulated extrudate was as in theprevious experimental series.

The results showed that, by addition of the granulates obtained inexperimental series 1 to 4, the starch content of the paper pulp in afibre slurry for paper manufacture could be adjusted to the desiredvalue without difficulty, with the result that a paper with goodresistance to tearing could be obtained without the need to add furtherstarch via a sizing press as a supplementary measure.

With the aid of the present invention, therefore, the sizing press andthe equipment connected downstream thereof, such as drying elements, maybe completely dispensed with, with the result that significantly moresimple and cheaper machinery for paper manufacture is feasible.

1. A medium for increasing the absorption capacity of paper pulp forstarch, comprising: at least one of cereal meal and starch; and apolymer with vinylamine units; said medium obtainable by mixing the saidat least one of cereal meal and the starch and the polymer withvinylamine units in an extruder.
 2. A medium according to claim 1,wherein the medium is obtainable by mixing cereal meal with 5 to 30 wt %of polymer with vinylamine units, with reference to the cereal meal, inan extruder.
 3. A medium according to claim 1 wherein the cereal meal isrye meal.
 4. A medium according to claim 1, wherein the starch is ryestarch.
 5. A medium according to claim 1, wherein the polymer withvinylamine units is a hompolymer and/or a copolymer.
 6. A mediumaccording to claim 1 containing rye meal and 5 to 30 wt % of polymerwith vinylamine units, with reference to the rye meal content.
 7. Amedium according to claim 1, wherein the polymer with vinylamine unitsis a completely hydrolysed homopolymer of N-vinylformamide.
 8. A methodof preparing a medium for increasing the absorption capacity of paperpulp for starch, characterised in that at least one of cereal meal andstarch, and a polymer with vinylamine units are mixed in an extruder. 9.A method according to claim 8, wherein water is additionally added. 10.A method according to claim 8, wherein water is added entirely orpartially in the form of water vapour.
 11. A method according to claim8, wherein rye meal is used as the cereal meal.
 12. A method accordingto claim 8, wherein the content of polymer with vinylamine units is 5 to30 wt %, with reference to the cereal-meal fraction.
 13. A methodaccording to claim 8, wherein a twin-screw extruder is used as theextruder.
 14. A method according to claim 8, wherein a completelyhydrolysed homopolymer of N-vinyl formamide is used as the polymer withvinylamine units.
 15. A medium according to claim 1, wherein cereal mealand/or starch and a polymer with vinylamine units for adjusting thestarch content in the paper pulp of a fibre slurry for papermanufacture.
 16. A method of paper manufacture, wherein a mediumaccording to claim 1 is added to the fibre slurry with the paper pulp.